During hydraulic fracturing operations, operators want to minimize the number of trips they need to run in a well while still being able to optimize the placement of stimulation treatments and the use of rig/fracture equipment. Therefore, operators prefer to use a single-trip, multistage fracturing system to selectively stimulate multiple stages, intervals, or zones of a well. Typically, this type of fracturing system has a series of open hole packers along a tubing string to isolate zones in the well. Interspersed between these packers, the system has fracture sleeves along the tubing string. These sleeves are initially closed, but they can be opened to stimulate the various intervals in the well.
As shown in FIG. 1, for example, a tubing string 12 for a wellbore fluid treatment system 20 deploys in a wellbore 10 from a rig 30 having a pumping system 35. The tubing string 12 has sliding sleeves 50 disposed along its length. Various packers 40 isolate portions of the wellbore 10 into isolated zones. In general, the wellbore 10 can be an opened or cased hole, and the packers 40 can be any suitable type of packer intended to isolate portions of the wellbore into isolated zones.
The sliding sleeves 50 deployed on the tubing string 12 between the packers 40 can be used to divert treatment fluid selectively to the isolated zones of the surrounding formation. The tubing string 12 can be part of a fracture assembly, for example, having a top liner packer (not shown), a wellbore isolation valve (not shown), and other packers and sleeves (not shown) in addition to those shown. If the wellbore 10 has casing, then the wellbore 10 can have casing perforations 14 at various points.
As conventionally done, operators deploy a setting ball to close the wellbore isolation valve (not shown) and positively seal off the tubing string 12. Operators then sequentially set the packers 40. Once all the packers 40 are set, the wellbore isolation valve acts as a positive barrier to formation pressure.
At this point, operators rig up the fracturing surface equipment 35 and pump fluid down the wellbore to open a toe sleeve 60 toward the end of the tubing string 12. This treats a first zone of the formation. Then, in later stages of the operation, operators selectively actuate the sliding sleeves 50 between the packers 40 to treat the isolated zones depicted in FIG. 1. In the most common approach, operators actuate the sliding sleeves 50 by dropping successively increasing sized balls down the tubing string 12. Each ball opens a corresponding sleeve 50 so fracture treatment can be accurately applied in each zone up the tubing string 12.
Several types of toe sleeves 60 have been used on tubing strings. In FIG. 2A, for example, a conventional toe sleeve 60, such as Weatherford's ZoneSelect toe sleeve, is a differential opening sleeve normally placed at the bottom or “toe” of the tubing string 12. The toe sleeve 60 is activated when a ball lands on a landing seat 73 on the sleeve's insert 70 and tubing pressure is applied against the seated ball to shear the sleeve's insert 70 free. The sleeve's insert 70 shifts in the housing 62, decreasing the enclosed volume 72. Once this occurs, the sleeve's insert 70 opens past ports 66 in the sleeve's housing 62 and locks in place so flow can be diverted to the wellbore through the open toe sleeve 60 from the housing's bore 64 and out the ports 66.
In FIG. 2B, another type of toe sleeve has a time delay, such as Weatherford's ZoneSelect Time Delay (TD) toe sleeve 60 used in a multizone completion system. Typically placed at the toe of a cemented completion, applied pressure ruptures a disc 68 in this TD toe sleeve 60, which exposes a piston 75 to differential pressure within the toe sleeve 60. The piston 75 moves slowly across concentric inner and outer ports 66a-b as the fluid being acted on is metered while passing from a primary chamber to a secondary atmospheric chamber.
The time-delay toe sleeve 60 is run in-hole as part of the tubing string 12. When the optimum setting depth is reached, tubing pressure is applied to check casing integrity and to rupture the disc 68 in the time-delay toe sleeve 60. In this way, the time-delay mechanism (i.e., piston 75, chambers, etc.) meters the toe sleeve's opening and eventually creates a pathway to begin stimulation operations. Depending on the application, the primary stimulation may be performed through the time-delay toe sleeve 60.
The time-delay toe sleeve 60 actuates at or below the casing test pressure, enabling the test pressure to be the highest pressure the system will be exposed to throughout operations. The time-delay toe sleeve 60 can avoid the inherent risk of a standard, hydraulically actuated toe sleeve 60 of FIG. 2A, which may open below a preset value (before pressure test is complete) or may require excessive pressure to open (exceeding casing and surface equipment limitations).
In FIG. 2C, another type of toe sleeve uses an atmospheric chamber to control opening, such as the Weatherford atmospheric chamber (AC) toe sleeve 60 used in a multistage completion system. The AC toe sleeve 60 is typically placed at the toe of the tubing string 12, and the AC toe sleeve 60 is actuated by applied tubing pressure creating enough hydraulic force on the sleeve's insert 70 to shear the insert 70 free of shear pins 76. The insert 70 within the AC toe sleeve 60 then slides past ports 66 in the sleeve's housing 62 and locks open. Preferably, the insert 70 opens upward to prevent a liner wiper dart from inadvertently forcing the sleeve 60 open during earlier operations.
The AC toe sleeve 60 is also run in the wellbore 10 as part of the tubing string 12. When the optimum setting depth is reached, tubing pressure is applied to actuate the openhole packers 40 and test the casing. Additional pressure is then applied to open the AC toe sleeve 60 and initiate communications to the formation for subsequent stimulation operations from the housing's bore 64 and out the ports 66.
In FIG. 2D, yet another type of toe sleeve uses a rupture disc to control operations, such as the Weatherford ZoneSelect Rupture Disc (RD) toe sleeve 60 shown used in a multizone completion. Placed at the toe of the tubing string 12, the RD toe sleeve 60 actuates when applied tubing pressure causes a disc 68 to rupture in the sleeve 60. The insert 70 inside the sleeve 60 then slides past ports 66 in the sleeve's housing 62 and locks in place. After the RD toe sleeve 60 is open, balls or composite plugs can be pumped down to begin stimulation operations. If required, the first stimulation operation can be performed through the open RD toe sleeve 60 from the housing's bore 64 and out the ports 66.
Another toe sleeve, such as the SMART toe sleeve 60 in FIG. 2E, allows the casing string to be tested to its full working pressure with an unlimited hold period and without exceeding the working pressure. Placed at the bottom or toe of the tubing string 12, the SMART toe sleeve 60, which is available from Weatherford, actuates and opens after two internal pressure applications. Once the SMART toe sleeve 60 is open, balls or composite plugs can be pumped downhole for subsequent stimulation.
The sleeve 60 includes a housing 62 with an insert 70 movable in its bore 64. The sleeve 60 has two shear features, including initiation shear screws 80 and arming shear screws 82. The initiation shear screws 80 are set for wellbore conditions, and the arming shear screws 82 have a predetermined value. Multiple low pressure tests can be applied to the closed sleeve 60 as long as the initiation valve for the initiation shear screws 80 is not exceeded. The first working pressure test shears the initiation shear screws 80, allowing the insert 70 to stroke and compress a wave spring 75. A snap ring 84 is partially collapsed during this stroke. After the first test, pressure is vented, and the load from the wave spring 75 shears the activation shear screws 82, which arms the sleeve 60 for the next pressure cycle. When working pressure is then applied, the insert 70 again strokes, which fully collapses the snap ring 84 so that it is no longer active. When the pressure is vented, the spring 75 then fully moves the insert 70 so that the ports 66a-b align allowing fluid communication out of the housing's bore 64 to the wellbore.
The SMART sleeve 60 can be used in horizontal and vertical wells, and in cemented and openhole completions. Because the SMART sleeve 60 does not open after the first pressure application, operators can maintain well integrity if issues arise at the surface. Each application of pressure can be held for an indefinite amount of time, enabling two opportunities to satisfy any regulatory requirements. The SMART sleeve 60 locks open, which prevents accidental tool closure caused by intervention tools.
Some implementations require that a tubing pressure test be performed for a specified period of time before wellbore fluid is introduced into the formation. As can be seen from the discussion above, some of the current toe sleeves 60 either open instantly or use a time delay by forcing hydraulic fluid through a restrictor device to slow the opening of the sleeve 60. Historically, oil wells have simply tested their tubing at a lower pressure than the pressure actually required to open the toe sleeve 60. Unfortunately, new leak paths can be created by increasing the tubing pressure to open the toe sleeve 60 above the test value used in the tubing pressure test. For this reason, more recent methods for opening toe sleeves attempt to delay the opening of the toe sleeve to allow a higher pressure tubing test to be performed before actually opening the toe sleeve. This overcomes the problems associated with over-pressurizing the tubing in order to open the toe sleeve.
Even though such systems have been effective, operators are continually striving for new and useful ways to open a toe sleeve downhole for fracture operations or the like. The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.